FIG. 1 shows a conventional receptacle for extension cord, which mainly includes a housing 10, a set of metal conducting strips 20, and a control switch 30. The housing 10 consists of a front cover 101 and a back cover 102 that are closed to each other, and is connected at a front end to a power cord 103, a distal free end of which is a plug 104 adapted to connect to an external power source. The set of metal conducting strips 20 includes a plurality of metal conducting strips, each of which is provided between two ends with a plurality of clampers. The metal conducting strips are separately fixedly seated in the housing 10 with the clampers separately aligned with slots provided on the front cover 101 of the housing 10. The metal conducting strips are directly or indirectly coupled with corresponding core wires of the power cord 103. The control switch 30 is mounted between the power cord 103 and one of the metal conducting strips for controlling an electrical connection of the external power source to the set of metal conducting strips 20. The following disadvantages are found in the above-described conventional receptacle for extension cord:                1. The receptacle for extension cord itself is a low-price product, and the control switch 30 is usually very expensive to prevent the receptacle from being manufactured at a reduced cost. The conventional receptacle for extension cord is therefore less competitive in the market; and        2. The core wires of the power cord 103 are connected to the set of metal conducting strips 20 and the control switch 30 byway of welding, which increases time and labor in assembling the receptacle to adversely affect the production efficiency of the receptacle.        
It is therefore tried by the inventor to develop an improved receptacle for extension cord to overcome the drawbacks existed in the conventional products.